This invention relates generally to variable flow valve assemblies and more specifically to an adjustable flow rate valve assembly for use with a liquid fertilizer sprayer implement.
This section of this document is intended to introduce various aspects of art that may be related to various aspects of the present invention described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the present invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
When agricultural liquids are applied to crops it is typically desirable to apply an ideal amount of liquid to each crop. Thus, for instance, when liquid fertilizer is applied to crops, to ensure that the crops grow at the same rate and are harvestable at the same time, it is desirable that the same amount of liquid fertilizer be applied to each crop. One way to apply an agricultural liquid to crops is by towing a liquid dispensing assembly behind a tractor through a field where the implement includes a wheel supported liquid container/tank, a manifold, a pump and valves. Here, the manifold typically includes an elongated member that forms a channel that is generally perpendicular to the trajectory of tractor travel through the field. In some cases the manifold will be 16 or even 32 crop row units wide and will form separate outlet apertures that generally reside above each of the rows that the manifold passes over during transport.
Valves are positioned at each of the openings and hence above each of the crop rows. Each valve includes a spring loaded needle member having a closure surface that is biased against a seat surface to close the valve. The valve is juxtaposed with respect to the manifold such that pressure within the manifold is applied to the closure surface. The pump pumps liquid from the container to the manifold and, when manifold pressure exceeds a cracking pressure, the manifold pressure forces the needle member into an open position and hence liquid is dispensed through the valve.
The rate of liquid dispensation must be controllable in most agricultural applications for two reasons. First, some crops may require more of the dispensed liquid than other crops and, indeed, even within a single field the same type of crop may require different amounts of the dispensed liquid in different sections of the field. Second, even where each section of a field requires the same amount of liquid, where tractor speed is varied, to deliver the same amount of liquid to crops, the rate of dispensing must be modified. For instance, where a tractor moves at five miles an hour and a first rate of dispensing occurs, if the tractor speed is increased to ten miles an hour, to dispense the same amount of liquid per meter within the field, the rate of dispensing likewise must be increased by 100%.
In the system described above rate of dispensing is generally controllable by controlling the pressure within the manifold. To this end, after a valve cracking pressure is exceeded, the size of the gap between a valve seat surface and closure surface changes as a function of the pressure within the manifold. Thus, as pressure within the manifold increases, the rate of liquid dispensed through a valve likewise increases.
One problem that has occurred with liquid delivery systems like the one described above is that it is expensive to manufacture valve springs that have identical loading characteristics. Where less expensive and less uniform springs are employed, the cracking pressures of the valves used on a single assembly may be very different and, indeed, the pressures that result in uniform opening of the valves may be different. Thus, as the manifold pressure is constant throughout the manifold, the end result when non-uniform springs are used within a valve is that the rate of dispensing with systems like the one described may be different for each of the valves on a system.
Thus, it would be advantageous to have a liquid dispensing assembly where valve construction enables a valve user to modify relative juxtapositions of valve components to compensate for different spring loading characteristics.